A 'Heat Pump' picture for the ENSO system

Dezheng Sun
Climate Diagnostics Center

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Why was the 1997-98 El Niņo so strong? Will El Niņo become more energetic in response to global warming? Why does the present climate have strong interannual variability in the first place? This talk will present observational and modeling results that shed new light on these fundamental questions. The observational results come from an analysis of the heat balance of the tropical Pacific over the last two decades. These results suggest that the magnitude of El Niņo warming should be proportional to the equatorial upper ocean heat content which is in turn proportional to the intensity of the equatorial surface heating. Numerical experiments with a coupled model in which the ocean component is a GCM and therefore explicitly calculates the heat budget of the entire upper ocean support this suggestion. To accommodate an increase in the equatorial surface heating, the ENSO system sucks more heat into the equatorial upper ocean with a stronger zonal SST contrast during La Niņa, and then pushes the heat poleward with a stronger El Niņo warming. In this heat-pump picture for ENSO, El Niņo acts as a regulator of the equatorial upper ocean heat content. Its existence and strength in the present climate owes not only to coupled wave dynamics, but also to the strong surface heating over the equatorial Pacific, and the high heat content the surface heating creates.

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4 Oct, 2000
3:30 PM/ DSRC 1D 403
(Coffee at 3:20 PM)
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